Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. In conventional overhead valve internal combustion engines, a pair of valves reciprocates in timed alternation to provide intermittent communication between the intake and exhaust manifolds and a combustion chamber. As is well known, the intake port of a combustion chamber is opened and closed by the reciprocating motion of at least one intake valve. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, an internal combustion engine has at least one exhaust valve and associated exhaust port for releasing expended combustion gases into the atmosphere. Lubrication is provided to the upper portions of the valves. Because temperatures in the combustion chamber may approach or exceed 1000 degrees Centigrade, any lubricating oil exposed to these temperatures will vaporize or burn leaving behind deposits that may interfere with the proper sealing of the valves and cause rapid deterioration. Valve stem seal assemblies are used to seal against leakage of oil between each valve guide and its associated valve stem.
It is therefore necessary to provide seals around the upper region of the valve stems and along the valve guide down to the manifolds and combustion chamber. A typical valve stem seal has a generally cylindrical shape that is partially closed at one end by the valve seal. The cylindrical region seats about the valve guide to maintain the valve seal in a stationary position. An upper region of the valve stem is surrounded by the valve seal when the valve stem is fully inserted into the valve seal assembly.
Conventional valve seal assemblies include individual body and seal components that typically must be assembled into the valve seal assembly. Use of multiple components and the associated assembly labor increases the cost of the valve seal assembly.
In some engines, unitary elastomeric valve stem seals are fitted over or atop each valve guide, wherein the seal component is frictionally mounted directly to the guide. However, traditional manufacture of such seals has been only on a unitary batch basis, or via one batch at a time. Thus, although much progress has been achieved in the art of valve stem design and construction, cost-effective techniques for enhancement of strength of materials, along with streamlined manufacturing techniques remain areas in need of additional improvement.